This invention relates to development apparatus for use with electrophotographic copying apparatus, or with electrostatic recording apparatus or the like, and more particularly to a dry type development apparatus for use with electrophotographic copying apparatus employing one-component developer.
In general, in electrophotographic copying apparatus, a photoconductor is electrically charged and is then exposed to the subject matter being imaged to form a latent electrostatic image thereof and in accordance with the electric potential of the latent electrostatic image, electrically charged toner is caused to adhere to the latent electrostatic image by a development apparatus. The developed toner image is then transferred to a paper and fixed thereon. Thus, copies are obtained by a typical electrophotographic copying apparatus.
As to the development apparatus in such electrophotographic copying apparatus, there are two types. One is for use with a so-called two-component developer comprising a toner and a carrier, and the other is for use with a so-called one-component developer comprising only a toner, that is, a developer without a carrier.
In the former development apparatus, it is necessary to incorporate a toner concentration controlling device for keeping the mix ratio of the toner and the carrier constant. Thus, it has some shortcomings, such as being complicated in mechanism, oversized or expensive.
The present invention relates in particular to the latter development apparatus for copying apparatus employing one-component developers.
As one-component developers, there are toner powders comprising resins and pigments, and magnetic toners comprising a mixture of resins and magnetic iron powders or comprising resins containing magnetic powders as the cores of the toners.
As a development apparatus for use with one-component developers, an apparatus having a movable rubber roller and a triboelectric charger positioned in pressure contact with the movable rubber roller has been devised. In this apparatus, insulating toner particles are accommodated in a vacant portion, or a hopper, formed by the rubber roller and the triboelectric charger.
With the rotation of the rubber roller, the toner particles are carried out of the hopper. At this time, a predetermined thickness toner layer is formed on the rubber roller and at the same time, the toner layer is charged triboelectrically with a predetermined polarity. The rubber roller is disposed in close proximity to a latent image bearing photoconductor or recording material and the triboelectrically charged toner particles are selectively supplied to the latent electrostatic image areas and thus the latent images are visualized.
However, this apparatus has the shortcoming that toner particles are dropped or scattered from the gap between the rubber roller and the triboelectric charger and thus many stray toner particles adhere to the latent electrostatic image bearing photoconductor or recording material. This is due to the manner in which the triboelectric charger is brought into contact with the rubber roller for sufficient triboelectric charging of the toner, with the triboelectric charger extending beyond the contact point with the rubber roller. In order to overcome the above shortcoming, the contact pressure of the triboelectric charger against the rubber roller may be increased, until the dropping or scattering of the toner particles is prevented.
However, the toner particles are coagulated or adhere to the surface of the rubber roller due to the increased contact pressure of the triboelectric charger. In this condition, it is impossible to separate the toner particles selectively from the surface of the rubber roller by the electric attraction of the latent electrostatic images formed on the photoconductor. Accordingly, as another shortcoming, good images cannot be obtained by this apparatus.
As in the above-mentioned development apparatus, with development apparatus in general use in electrophotographic copying apparatus, toner is electrically charged by a triboelectric charger at the time or immediately after the toner is deposited on the surface of a development roller, and is then brought into near or actual contact with a photoconductor. However, the condition of the toner layer formed on the peripheral surface of the development roller is changed delicately depending upon the shape of the triboelectric charger. More specifically, the shape of a triboelectric charger has a great effect not only on the formation of the uniform toner layer on the development roller but also on the replenishment of toner and accordingly, it affects various qualities of developed image. Further, depending upon the number of triboelectric chargers, the saturation time of the potential of charged toner is greatly effected.